Vocab 1 Flashcards
The study of radiative transitions between the stationary energy states of an atom or molecule.
spectroscopy
Particles of energy radiating from a source and characterized by an electromagnetic wave
photons
The spatial period of an electromagnetic wave, i.e. the number of units of length per wave,
characterized in units of distance, e.g. Å, nm, μm, mm, cm, m, km, etc.
wavelength
The number of waves per second, i.e. n in s-1. A quantity directly related to the energy
difference between two stationary energy states, e.g. ΔE = h ν .
frequency
The spatial frequency of a wave, or number of waves per cm, equal to the reciprocal of its wavelength in cm. a term that describes the energy involved in an atomic or molecular transition, expressed in units of cm-1.
wavenumber
The amount of energy gained by the charge of a single electron moved across an electric potential difference of one volt; equivalent to 1.6021 ́ 10-^19 J.
electron volt
The simplest wave form for which the profile is a sine or cosine curve with a specified frequency and period
harmonic wave
graphical representation of an object moving with simple harmonic motion
circle of reference
the amount of time it takes for one complete wave to pass a stationary point
period
The scalar measure of rotation rate and is the magnitude of the vector quantity angular velocity, expressed in radians per second
angular frequency
An angle measured relative to the x-axis of the circle of reference that specifies the displacement and direction of propagation of a wave.
phase angle
The phase angle at t = 0.
initial phase angle
Waves that oscillate perpendicularly to the direction of propagation, i.e.
electromagnetic waves.
transverse wave
Waves that have the same direction of vibration as their direction of propagation, i.e. acoustic waves.
longitudinal wave
When two or more waves traverse the same space, a disturbance occurs that is the sum of the disturbances caused by the individual waves; the resulting electromagnetic disturbance is the algebraic sum of the individual constituent waves.
principle of superposition
The difference in the absolute phase angles of two electromagnetic waves, δ =φ2 −φ1 ; also defined as the amount by which one sin wave leads or lags another sin wave ; can be measured in degrees or radians.
Relative Phase Angle / Phase Shift / Phase Difference
two electromagnetic waves for which the phase difference δ is zero
coherence
The interaction of light waves to yield a resultant irradiance that is different from
the sum of the component waves
optical interference
Two electromagnetic waves having a phase difference d of 0° or 360°, or an
integer multiple of 360°, occurs when δ = 0, ± 2π , ± 4π , etc. radians.
constructive interference
Two electromagnetic waves having a phase difference d of 180° or 180° plus an
integer multiple of 360°
destructive interference
The description of how any general function or periodic waveform can be
approximated by the summation of simpler sine and cosine terms.
fourier analysis
stable provider of radiant energy
source
Device that discriminates polychromatic source energy into individual wavelengths.
wavelength selector
Device that converts radiant energy into an electrical signal, or other physical property, e.g. heat or resistance, that can be measured.
radiation detector
A source of electromagnetic radiation whose spectral energy distribution is a function of both temperature and wavelength.
black-body radiator
The flux of radiation in waveband d l escaping from a hole of unit area into a unit solid angle.
luminescence
The cone generated by a line that passes through the vertex and a point moved along the periphery of the surface of the sphere; units = steradians (sr).
solid angle
Relationship describing how the absolute intensity of the energy emitted from a black-body source increases, and the wavelength maximum of the distribution shifts, toward shorter wavelengths.
wien displacement law
The ratio of the spectral radiance of a source to that of a black-body radiator at the same wavelength and T.
spectral emissivity
A source whose spectral emissivity is less than one.
gray body
An filter that uses the principles of optical interference to transmit a narrow band of measurement wavelengths. an optically resonant cavity formed by two partially reflecting mirrors that are non-absorbing and therefore transmit the light that is not reflected.
Fabry-Perot Filter
substance that is a poor conductor of electricity, but that can be polarized by an applied electric field; a term that describes materials with a high polarizability, including many glasses and optical materials.
dielectric material
A filter that transmits radiation with a certain range of wavelengths and attenuates or blocks wavelengths outside that range.
bandpass filter
A filter that absorbs all radiation shorter than a given wavelength, and passes all radiation longer than this wavelength – also called a “long pass” filter.
Short-Wavelength Cut-Off Filter
A filter that absorbs all radiation longer than a given Wavelength, and passes all radiation shorter than this Wavelength – also called a “short pass” filter.
Long-Wavelength Cut-Off Filter
The variation of the index of refraction of a medium with the wavelength of the incident radiation
dispersion
The ratio of the speed of an electromagnetic wave in a vacuum to its speed in an arbitrary medium other than vacuum
index of refraction
The description of how a light ray changes direction at a single surface between two media with different refractive indicies
snells law
The change in reflected angle with the change in wavelength
angular dispersion
The linear separation of two wavelengths in the focal plane of a monochromator
linear dispersion
The difference in the wavelengths of two lines divided by the observed separation of these lines in the focal plane of a monochromator
reciprocal linear dispersion
The ability to separate adjacent absorption bands or spectral lines; the
smallest discernable difference in wavelength
resolution / resolving power
The generally accepted criterion for determining whether two adjacent spectral lines are fully resolved; defined as the central maximum of the first spectral line falling on the first minimum of the second line; practically measured as a ~19% minimum between two equally intense lines.
rayleigh criterion
The limiting case where light approaching the diffracting object is parallel and monochromatic, and where the image plane is at a distance large compared to the size of the diffracting object. consists of a central maximum peak with side peaks of gradually decreasing intensity.
Fraunhofer Diffraction
plane surface consisting of a large number of very small, parallel, equally spaced grooves, at which different wavelengths constructively interfere at specific angles, leading to an angular dependence of intensity maxima, according to the grating equation
diffraction grating
The integral multiples of the wavelength, m, that satisfies the grating equation and assumes the values 0, ±1, ±2, etc.
order of diffraction
The density of grooves in the diffraction grating equation, d ; usually denoted in units of grooves mm-1.
groove spacing
The multiple wavelengths l that satisfy the grating equation and appear at a given diffraction angle β for a given groove spacing d, and a given angle of incidence α
overlapping orders
The range of wavelengths diffracting from the grating for which no overlap of adjacent orders occurs.
free spectral range
A grating that has its groove facets titled at a particular angle with respect to the flat surface plane of the grating.
blazed grating
The angle the grating groove facet is tilted with respect to the flat surface plane of the grating ; geometrically equivalent to the angle between the normal to the grating and the normal to the groove face.
blaze angle
The first-order wavelength corresponding to the m = 1 diffracted radiation from a blazed grating.
blaze wavelength
Very coarsely ruled (~100 grooves mm-1) gratings with very large blaze angles designed to be used in special monochromators with large diffraction angles and high orders to achieve high resolution.
echelle grating
Widely used dispersive instrument used to optically isolate single wavelengths from a polychromatic source.
monochromator
Dispersive instrument used to optically isolate multiple wavelengths simultaneously from a polychromatic source. implies multiple single element detectors located at multiple exit slits in the instrument
polychromator
An instrument used for dispersing electromagnetic radiation from a polychromatic source into its component spectrum. Can also refer to a dispersive instrument, e.g. a Czerny-Turner monochromator, in which the single element detector at the exit slit is replaced by a multichannel detector that records large segments of the spectrum at once in the focal plane of the instrument.
spectrograph
Common monochromator design in which a broad band illumination source is aimed at an entrance slit. The amount of light energy entering the monochromator is defined by the slit geometry and the acceptance angle of the optical system. The slit is placed at the effective focus of a curved collimating mirror so that the light from the slit reflected from the mirror is collimated. The collimated light is diffracted from the grating and then is collected by the final focusing mirror that refocuses the light, now dispersed, onto the exit slit.
Czerny-Turner monochromator
The half-width of the wavelength distribution passed by the exit slit of a monochromator
effective bandwidth
The angle φ that the diffracted ray makes with respect to the optic axis in a monochromator.
takeoff angle
The angle θ that the grating makes with respect to the optic axis in a monochromator, as measured from the normal to the grating surface
grating rotation angle
common mechanical drive mechanism for monochromators in which l is directed proportional to sin q , therefore the distance the lead screw is moved is directly proportional to wavelength
sine bar drive
The convolution of the entrance and exit slit images resulting in the shape of the instrument profile in a dispersive grating monochromator.
slit function
